SIOUX FALLS, S.D. -- Five years ago, when he walked in the mornings past the men and women who stood outside his office building with picket signs that called him a murderer, Buck Williams liked to think that at least he was not the only physician for 300 miles who publicly took in abortion patients. In western South Dakota, across the state from Williams's office in Sioux Falls, obstetrician Ben Munson had been doing abortions since before they were legal; in Sioux City, Iowa, due south and just over the state border, women from southern South Dakota and northern Iowa reported for their abortions to another obstetrician, Lee Van Voorhis.

That was the roster, for a pregnant South Dakota woman who wanted an abortion without driving deep into another state -- three doctors. Then Ben Munson retired at 70 from active practice, so now there were two.

Then directors at St. Luke's Regional Medical Center, the Sioux City hospital where Van Voorhis did most of his abortions, decided the hospital would no longer allow elective abortions on the premises. His own partners, a group of ob/gyns who had unenthusiastically accepted his abortion practice without doing the procedure themselves, said they wanted him to stop doing even early abortions in the office. And so Van Voorhis, with some regret and no small amount of relief, decided he was through with abortions, too.

"I guess I said to myself that I was just tired of it," Van Voorhis says. "I had kind of grown weary of the pressure, or the turmoil. I had given it a good effort. I had done it long enough. And if it was going to be available, it was going to be up to someone else to provide the service."

So now there was one -- one doctor, in his mid-fifties and beginning to think about retirement, providing the only elective abortions in the state of South Dakota.

Williams worked in the heart of the Sioux Falls medical complex, in a big modern building with a lot of other doctors. Then in 1988, he moved across town because the medical building lease had been rewritten to specify that no abortions could be performed in the tenants' offices. He found a veterinary clinic, quite a nice place once it was remodeled, and he made certain before signing his new lease that his landlord knew everything possible about Williams's line of work.

In 1989, after having done business with Buck Williams for 17 years, his office laundry service stopped washing his linens. The drivers, Williams was told, did not want to come to his office any more. The laundry owners decline to speak publicly about Williams' service, but the director of a local anti-abortion counseling center says the story among her colleagues was that an elderly woman with a picket sign had asked a driver, at the entrance to Williams's clinic, "How do you feel about picking up this laundry for this man that has been killing babies?"

Buck Williams uses a lot of paper linens now. His wife Joan, who runs the office, sometimes takes towels home with her to wash in the family machine. The National Abortion Federation will be holding a symposium this month on what NAF director Barbara Radford calls "the very serious physician shortage," but nobody needs to provide convincing detail to the only abortion doctor in South Dakota.

Women come to Williams's office from five states and sometimes Canada; they come by bus and by car, through rainstorms and Dakota blizzards, some of them driving themselves the six hours it takes to reach Sioux Falls from Rapid City. They come because they have heard his name, or seen his yellow pages ad, or written down the address given them by their own doctors -- scores of physicians in South Dakota will refer to Buck Williams, but nobody else will actually do what he does.

"It's the sleeve-pullers," Williams says, and does a quick mime of a person sidling up and whispering from the side of his mouth, afraid to be overheard. "They pull on your sleeves and they say, 'Hey, I'm with you, but I can't say anything, because my colleagues are all Catholic.' "

That Williams lives just outside Sioux Falls, a mere car ride away from the office, gives his clinic a modest advantage over some. Up in Fargo, where the last North Dakota abortion doctor retired in his mid-seventies in January, patients sometimes arrive at the Women's Health Organization after a six-hour drive and then learn that the day's abortions have all been postponed because bad weather grounded the airplane that was bringing in the doctor.

The clinic in Duluth, Minn., brings its doctors by plane too, so women from the northern part of four states -- Minnesota, Wisconsin, North Dakota and Michigan -- depend for their abortions on the day's flying conditions.

Susan Hill, founder of a North Carolina company that owns abortion clinics around the country, says three of her nine facilities are in cities where every physician in town refuses to accept abortion patients.

"State restrictions are the least of our problems," says Hill. "We're worried more about getting in and out of the clinics every day safely, worried about getting physicians to come to work, worried about protecting our staff and our patients. I think the lack of availability of physicians and places to perform abortion -- real estate -- are the two biggest problems providers face in the future. And both of them are make-or-break factors."

Last fall, after $300,000 worth of improvements to a newly rented facility, Hill's clinic in Raleigh, N.C., was evicted four months after moving in; she says that during the office remodeling, someone left fetus pictures in the building's public bathrooms, and that all phone lines to the building were cut the night before the clinic opened.

"We're going to lose the investment on the improvements," she says. "You can go to court and fight it, but the problem is, that's tremendously expensive, and it can be dragged out for years. We're going to solve it this time -- we're going to buy our new building. That's the only thing we can do."

When she first began opening her clinics 15 years ago, Hill placed them in smaller cities of the South and Midwest, a long way from the more abortion-tolerant climates of urban areas like Washington or Los Angeles. Those large metropolitan regions offered established abortion facilities 20 years ago and still do today; a recent survey by the Alan Guttmacher Institute, a research organization formerly funded by Planned Parenthood, found that over the 1980s, the number of abortion providers in metropolitan counties dropped only slightly -- a decrease of 6 percent from 1982 to 1988.

But in more rural parts of the country, according to the Guttmacher study, the number of doctors and medical facilities willing to accept abortion patients dropped 51 percent from 1977 through 1988. Many hospitals -- like the Sioux City medical center where Lee Van Voorhis had done abortions until picketers began gathering out front and suggesting a community boycott -- have changed their rules to allow only medically necessary abortions onsite.

Eighty-three percent of American counties now have no doctor who will acknowledge performing abortions, and in some states those counties hold a large number of women: in Arkansas, Kentucky, Mississippi, West Virginia and South Dakota, according to the study, three quarters or more of the state's women live in counties where there is no doctor like Buck Williams.

"It's starting to look bad everywhere, except the District of Columbia -- I can't think of a state where there isn't a problem," says the National Abortion Federation's Barbara Radford, whose organization represents abortion facilities and has joined with the American College of Obstetricians and Gynecologists to arrange this month's symposium on what seems to be the increasing reluctance of physicians to participate directly in abortion. "Our members tell us they're having a difficult time finding well-trained, qualified physicians to provide abortion services. Women calling the hotline are telling us they have no provider within their own community," Radford. Silent Support

At the Lovejoy Surgical Center in Portland, Ore., patients sometimes drive eight hours from Boise because Glenn Weyhrich, the only doctor in Idaho who will do an abortion past 12 weeks of pregnancy, has a full ob/gyn practice with a one-month wait for appointments. In New York, a Manhattan gynecologist, Amy Cousins, makes a weekly 3 1/2 hour drive to the town of Vestal in the western part of the state, where all but one of the region's physicians have declared in the last few years they will no longer accept abortion patients; in each two-day stay, Cousins says, she does 40 to 50 abortions for New York and northern Pennsylvania women.

"It doesn't take the elimination of very many of us to produce a situation of no access," she says. "It's a very thin line. I broke my arm last year, and I worked the entire time with a broken arm. What could I do? I couldn't stop. I can't leave them."

And at the Utah Women's Health Center in Salt Lake City, administrators recently turned to a professional placement firm after searching for a year for a third physician willing to do large numbers of abortions.

"This is going to be a hard fill," says Sharon Drake, a medical staffing specialist with the Chicago firm of Spencer Roberts & Associates, which is trying to help the Women's Health Center find a gynecologist. "It's going to be a very difficult interviewing process. Thank God I don't have to do it face to face."

Drake says her company has had limited success placing physicians into general ob/gyn practices where private patients occasionally receive abortions. It is the facilities themselves, the clinics that offer various gynecological services but draw most of their patients for abortions, that Drake says the doctors she interviews are usually quicker to reject. "I'll say, 'How do feel about a place that has a high level of terminations?' " says Drake. "And he knows. He knows what I'm saying."

It is not that most of the doctors Spencer Roberts works with are entirely opposed to abortion. The firm currently holds biographical data on about 500 ob/gyns. The ranks of those who believe abortion kills human beings certainly include physicians, but Spencer Roberts' director Jacqueline Spencer says most of the ob/gyns she talks to say they believe their patients ought to be able to decide for themselves about abortion.

The most recent ACOG survey on abortion attitudes largely backs this up; in 1985, 84 percent of doctors surveyed said they thought first-trimester abortion was acceptable in certain circumstances; of those, three fourths thought "mother's personal choice" was reason enough.

But asking the doctors to perform the abortions themselves is a different matter, particularly in places where openly bringing in even a few abortion patients attracts demonstrators determined to call attention to what they see as the murder of babies.

South Dakota is a place like that, as Buck Williams has spent 17 years learning over and over again; Williams remembers what now seems to him his thoroughly nai ve first speech at a Sioux Valley Hospital staff meeting, when in the wake of the 1973 Roe v. Wade decision he suggested the hospital begin accommodating abortions.

"And the funniest thing happened that I'd ever seen," he says. "Nobody wanted to take a stand, one way or the other. Everybody went for the phone or had their beeper go off or some damn thing. By the time the vote would have come, there were like four people left out of 150." The Abortionist Label

Williams himself held off at first on performing abortions, he says. For many years, he had strongly believed that women who wanted to end pregnancies needed a medically sound place to go; as a medical student in New York, he says, he stood at the bedside of a young Puerto Rican woman who had tried to induce her own abortion by eating a kind of rat poison that irreversibly destroyed all her organ systems. "Finally she did abort," Williams says, "just before she died. That was the patient where I remember saying, 'This is wrong. This is absolutely wrong.' "

He was not willing to break the law, though, and even after 1973, Williams referred women who wanted abortions to physicians like Ben Munson, or the reputable doctors who were doing abortions in Kansas.

By 1981, Williams says he had become convinced that he could safely manage abortions in his own office, too, and he went to Iowa City and Minneapolis to train with doctors experienced in elective abortion. Williams was an active obstetrician then, and he says he had hoped simply to add abortion to the services he offered his patients. "But the other side sees to it immediately," he says, "that you are the town abortionist."

In fact, what happened to Buck Williams after his practice in abortion went public was low-key compared to the protest in some other cities. Nobody bombed his office. No picketers came to his home. One Easter, Buck and Joan Williams went to Lutheran services and found 800 crosses in a ditch beside the church, with a sign indicating that each cross represented one baby whose life Williams had taken the previous year, but Williams was not shunned in church; many parishioners told the Williamses they thought the display was offensive.

But picketers came to his medical building, sometimes a few, sometimes a large group. Somebody apparently looked up Williams's birth certificate and wrote him angry letters referringto his place of birth and parents' names. People began calling and writing to his employees, talking about infant murder and urging them to resign and, at one point, protestors visited his staff's neighborhoods and distributed postcards that displayed an aborted fetus's decapitated head. "I'm going to tell you," Williams says, "this is not an easy way to practice ob/gyn."

None of this went unnoticed in the Sioux Falls medical community, either. There were doctors who said abortion should be prohibited and doctors who said they knew the procedure itself was something they simply did not want to do -- that they had studied obstetrics to help produce life, not end it. But among the doctors who philosophically agreed with Buck Williams, a kind of self-feeding cycle was under way, one now common in many states besides South Dakota: Abortions are singled out as being unlike other medical treatment, which makes doctors stop including them as part of their wider practice, which in turn isolates abortion even more from the mainstream of medical care.

A young obstetrician-gynecologist who trained with Buck Williams and still refers patients to him says that in his own town, about 90 minutes' drive from Sioux Falls, an imaginary warning flag would rise above the office of any doctor known to grant the occasional patient's request for an abortion.

"You get labeled, at least most of the time, as an abortionist," the doctor says. "Right there, if 35 percent of the people don't believe in abortion -- even if you're the best-trained doctor for their particular problem, they'll probably ask to see another doctor."

Four years ago, an obstetrician-gynecologist named Robert George moved to Sioux Falls with some abortion experience in his own background; George had worked in Army hospitals where abortion was part of the gynecological service, and he says that when he first came to South Dakota he thought that was a reasonable posture for someone who was supposed to be providing health care for women. "That's part of providing health care for women -- to offer them that option, if they want," George says.

But George set up practice in the Sioux Falls medical complex, and he saw Williams's picketers, too; until Williams moved, every doctor in the building walked past the men and women with the pamphlets and signs. George says he thought about the non-abortion patients those picketers might turn away, patients willing to switch physicians solely to avoid encountering demonstrators. He thought about his children and the things he believed they might hear from people who believed abortion was the same as killing. And he joined the ranks of what he thinks of as Williams's silent supporters -- the doctors who will send him patients, who speak highly of his reputation, but will not do the abortions themselves.

"We're silently, chickenly, cowardly, however you want to label us, prochoice," George says. "If it was just me -- if the price was just me and my wife -- I'd go ahead and do them. But the price has got to be paid by the kids, and that's not fair. I'm not going to subject my family to this."

Buck Williams says his children have never complained about much harrassment, although they were finishing high school by the time his practice got under way. George's children are much younger, and he envisions them coming home from school, as the Iowa doctor Lee Van Voorhis's children sometimes did, on the days when a schoolmate announced that their father killed babies. "How do you explain this issue to children?" George asks. "Everything is black and white to them. There are no shades of gray. Maybe when they're in high school they'll understand this, but how do you explain it to a 6- or 7-year-old? 'Daddy, are you a killer?' "

There are abortion opponents in Sioux Falls, of course, for whom the answer to that question is clear. "That's why I tell people to continue to picket," says Leslee Unruh, the director of a Sioux Valley center that counsels pregnant woman away from having abortions. "That's the hot button. That's the pressure. And that's why we're going to see doctors being picketed more and more in their homes."

Unruh says she follows abortion rights literature and knows what has happened in places like South Dakota -- "that they're having a hard time finding abortionists," she says. "That's music to my ears. So I know it's working. That's what they're angry about. It's working."

Neither Buck nor Joan Williams would disagree; half of Williams's patients visit him for non-abortion gynecology, but Joan Williams has had new patients ask anxiously what the doctor looks like, evidently envisioning the kind of unsavory person still suggested by the term "abortionist."

"The opposition has had some successes, sure," she says. "They've almost succeeded in recriminalizing abortion, simply by making people having them feel like criminals."

And although no statistical studies offer much evidence, there is a feeling among many abortion doctors that a kind of generational gulf has opened between the professionals of Buck Williams's era and the doctors coming behind them -- doctors who never worked at a time when their hospital duties involved trying to keep alive women whose illegal abortionists had bungled the job.

"It's unfortunate that they cannot conceive of that kind of situation, because I think many of them, were they aware of what women went through in those years, would be abortion providers," says University of Iowa obstetrics and gynecology professor Charles A. deProsse. "I don't think there's any question but that the younger generation of practitioners is much like the younger generation of women who just say, 'Well, you know, abortion's always been available and always will be,' without realizing the tenuous nature of its availability to them."

DeProsse is 64, nearly a decade older than Buck Williams; it was under deProsse's tutelage that Williams began learning what he believed he needed to know about abortion and possible complications. He says he assumed other doctors would join him -- that it never occurred to him, when abortion was legalized, that 17 years later he might find himself the sole South Dakota doctor to take abortion patients in.

"It's wrong -- it's terribly wrong," Williams says. "There needs to be a person in every population center, I would say. Ideally, there should be about a half-dozen physicians providing abortions in this state. And it scares me now, because yes, it's the safest operation going, but it's not an operation that is totally without complications. No operation is totally without complications. And I have a concern that somebody's going to go home sometime and not seek the medical attention they need or not have a regular source of it . . . There are hundreds of doctors in this state who have no idea their patients have had abortions, because the patient won't tell them."

He knows he is not immortal, either. Williams turned 56 last winter, and without some shift in South Dakota's medical climate, his own retirement could change his state's abortion picture as quickly and completely as any state law. "I feel I have a moral obligation, if I can, to find someone to take my place," he says. "It makes no difference if it's legal or illegal, if there are no providers."